The perception of the phytohormone, ethylene, by plants constitutes a mechanism by which plants response to environmental changes and other phytohormones. The EIN3 locus, which acts in the ethylene signaling pathway, has been identified using mutation analysis of Arabidopsis thaliana and cloned from a T-DNA tagged mutant. A second-site mutational analysis is proposed and both enhancers and suppressors are sought in hope to find new loci involved in the ethylene signaling pathway. Classical mutational analysis is not going to saturate Arabidopsis genome and to identify all the components in the ethylene signaling pathway. Therefore yeast two hybrid selection system is proposed to find additional players in this pathway. It is hoped that these studies will shed light on the molecular mechanisms by which ethylene and other plant hormone signals are transduced.